Composite structures produced from metal substrates having a ceramic enamel surface layer and plastic materials are known (see, e.g., U.S. Pat. No. 4,664,982). Such composites are typically used in various plumbing applications (e.g., such composites may be used as bathtubs). In such plumbing applications, the composites must be able to resist delamination over extreme temperature ranges (e.g., from -15.degree. C. to 100.degree. C.). Typical of the plastic materials used are unsaturated polyester resins, epoxies, polyurethanes, isocyanurates, and nylons. U.S. Pat. No. 4,664,982 describes the use of a variety of different silane materials as adhesives to assist in adhering the plastic material. In addition, composites of a wide variety of different substrates with foam materials are known (see, e.g., U.S. Pat. Nos. 3,496,058 and 4,053,545).
Solventless spray systems are also known (see, e.g., U.S. Pat. No. 4,695,618).
Polyurethane elastomers and adhesives having improved sag resistance are known. Such systems are typically cured using a diamine curing agent (see, e.g., U.S. Pat. Nos. 3,714,127, 3,932,360, 3,979,364, 4,444,976, 4,552,934, 4,743,672, and 4,876,308).
A commercially available system for application to a substrate was based upon a reaction mixture of: i) 86.8% by weight of a 455 molecular weight triol formed from propylene oxide and trimethylolpropane, 6.0% by weight of a 28 OH number triol from glycerin, propylene oxide and ethylene oxide (and having 82% primary hydroxyl group content), 2.3% by weight of xylene diamine, 4.7% of a moisture absorbing zeolite, and 0.2% of a tin catalyst, and ii) an isocyanate terminated prepolymer from an isocyanate and a polyether, having an NCO content of 27.4% by weight.